1. Field of the Invention
The present invention relates to an opto-electric hybrid board including an optical waveguide and an electric circuit board which are stacked together.
2. Description of the Related Art
With the increase in the amount of transmission information, optical interconnection in addition to electrical interconnection has been used in recent electronic devices and the like. As an example of such a technique, an opto-electric hybrid board has been disclosed in Japanese Laid-open Patent Application Publication No. 2011-48150. As shown in FIG. 6, this opto-electric hybrid board includes: a flexible circuit board E0 including a flexible substrate 51, and electrical interconnect lines 52 formed on the front surface of the flexible substrate 51; and an optical waveguide (optical interconnect lines) W0 (including an under cladding layer 56, a core 57 and an over cladding layer 58) made of epoxy resin and the like and stacked on the back surface (a surface opposite from the surface with the electrical interconnect lines 52 formed thereon) of the flexible substrate 51 of the flexible circuit board E0.
However, when an optical element is mounted on the flexible circuit board E0 of the aforementioned opto-electric hybrid board, both the flexible circuit board E0 and the optical waveguide W0, which are thin and flexible, are deformed by the load applied during the mounting process. This makes the mounting process difficult, resulting in poor workability during the mounting process. Additionally, there is a danger that light propagation losses are increased due to the aforementioned deformation.
Another opto-electric hybrid board, on the other hand, has been disclosed in Japanese Laid-open Patent Application Publication No. 2009-265342. As shown in FIG. 7, this opto-electric hybrid board includes a stainless steel layer M0 provided entirely between the flexible circuit board E0 and the optical waveguide W0. In this opto-electric hybrid board, the stainless steel layer M0 serves as a reinforcement to suppress the deformation resulting from the load applied during the process of mounting the optical element. Thus, this opto-electric hybrid board is excellent in the mountability of the optical element, and is small in light propagation losses due to the aforementioned deformation.
Recently, there has been a need for the size reduction of the aforementioned electronic devices and the like. Accordingly, a need has arisen for the use of such an opto-electric hybrid board in a small space. For such needs, it is necessary that the opto-electric hybrid board is made flexible and stored in a small space. In the opto-electric hybrid board including the stainless steel layer M0 provided entirely as mentioned above (with reference to FIG. 7), the stainless steel layer M0, however, acts as an impediment to making the opto-electric hybrid board flexible. Such a conventional opto-electric hybrid board still has room for improvement in this regard.